1. Field of the Invention
The present invention relates to a controller for a storage device, which is capable of modifying or customizing firmware for controlling I/O operations relating to the storage device.
2. Description of Related Art
Recently, a controller for controlling I/O operations of a magnetic disk drive, for example an SCSI (Small Computer System Interface) disk controller for a hard disk drive having a large capacity memory, has been equipped within the drive. The drive has ROM based firmware for controlling I/O operations thereof. When new functions are defined or customization is required, the ROM must be changed or a new one added. In addition, new firmware, which is stored in ROM, must be developed and tested at the factory without the benefit of customer application testing before the drive may be tested at the customer site.
Generally, as mentioned above, firmware in ROM must be changed when upgrading, modifying, or developing new firmware. These requirements cause the time for a production change to be long, and bring higher manufacturing/field support costs.
As a possible improvement, new firmware can be stored in external memory. However, such firmware can too easily be written over, for example by a conventional write command, since it is not specially protected. This also brings higher manufacturing/field costs as the external memory must be provided. Moreover the external memory causes deterioration in the functioning of a bus which connects a host system and the drive. Since, for example, an SCSI bus is limited as to the number of host systems and/or drives that can be connected to it, it is undesirable to provide such an external memory.